NYU School of Medicine and collaborating clinical and basic investigators in Medicine and Pathology propose to establish the Translational Center of Molecular Profiling in Preclinical and Established Lupus (COMPEL) comprising 3 Projects, 2 Research Cores, and an Administrative Core. The overarching goal is to elucidate the mechanisms by which Systemic Lupus Erythematosus (SLE), a prototypic yet clinically and immuno- molecularly heterogeneous autoimmune disease, is initiated and perpetuated. COMPEL leverages a) a unique cohort of asymptomatic women presenting with breakdown in B cell tolerance identified because of neonatal lupus (NL) in an offspring (Research Registry for Neonatal Lupus, RRNL) and b) a robustly phenotyped cohort of established SLE patients spanning diverse racial backgrounds and with a high penetrance of serious illness (NYU Cohort). Project 1 profiles anti-Ro preclinical and clinical autoimmunity to identify blueprints of an immune system that remains preclinical, and in individuals who have progressed to overt disease. The approach rests on identifying associations between host genetics, the microbiome, and the phenotype of CD4+ T cells, which constitute an immune triumvirate of T cells, antigen-presenting cells with an MHC II-defined specificity towards particular microbial taxa, and B cells. Project 2 explores microbiome pathobionts and SLE pathogenesis to understand how specific candidate pathobiont bacterial isolates contribute to overt SLE disease and flares, and to peripheral blood expansion of disease-associated B cell clones. Human intestinal IgA responses can be both specific for in vivo eliciting bacteria, and often cross-reactive with self-antigens. Yet, the gut-associated B cell response has not been investigated in SLE as a driver of autoimmune disease. Project 3 focuses on DNASE1L3, a unique secreted DNase that is essential for protection against SLE. We have shown that DNASE1L3 digests DNA in circulating microparticles and antibody (Ab) reactivity to microparticle antigens is frequently detected in SLE. The project will explore Ab responses to DNASE1L3- sensitive microparticle antigens in preclinical and established SLE patients; molecularly characterize these antigens and test DNASE1L3 as a therapeutic. The Research Technology Core brings advanced technology for NGS applications of large scale autoAb gene repertoire analyses from human B cell samples and will sort intestinal IgA-coated bacteria profiled by 16S rRNA microbiome surveys. The Clinical Core comprises the database (REDCap) and biobank (Freezerworks) of 3 cohorts (RRNL, NYU Lupus Cohort, healthy controls) to facilitate translational studies. The Administrative Core supports organizational, financial and reporting activities. The analytic team brings expertise in biostatics, genetic statistics, bioinformatics and computational science. External advisors covering translational SLE, the microbiome, T cell biology and mucosal immunity, and 2 lay persons with ties to NL, will provide overall review and with COMPEL select Pilot/Feasibility Projects to leverage program resources and expand thematic objectives.